Richard L. Garwin March 17, 1999
Effectiveness of Proposed National Missile Defense Against
ICBMs from North Korea
(For distribution to Congress and the Press)
The NMD system under development by the Defense Department,
according to Lieutenant General Lester L. Lyles, USAF, Director of
the Ballistic Missile Defense Organization (02/24/99) "would have
as its primary mission the defense of all 50 states against a
small number of intercontinental-range ballistic missiles launched
by a rogue nation." But General Lyles goes on "Such a system
would also provide some residual capability against a small
accidental or unauthorized launch of strategic ballistic missiles
from China or Russia. It would not be capable of defending
against a large-scale, deliberate attack."
A Deployment Readiness Review is to be held in June 2000 to
"assess whether or not the technical progress has been made which
would allow more senior decision-makers to decide whether or not
we should commit to deployment," which decision would be made
apparently at about the same time.
But the United States should not commit to deploying a system that
will not do the job. First, the job against North Korea or other
emerging ICBM threat, possibly from Iran or Iraq.
In this regard, the nation should heed the CATO Institute Foreign
Policy Briefing No. 51 of 02/11/99,
"Rather than throw money at the program-- as would some
conservatives to whom missile defense is a religion-- or
completely avoid the missile defense issue-- as would some
liberals enamored with arms control for its own sake-- the
best policy is to honestly assess the nature and extent of
emerging threats and develop a national missile defense
system at a pace that the technology can support and that
test results will bear out. No matter what the threat is,
rushing to develop a system that fails to work is not an
attractive remedy"
Unfortunately, the proposed NMD system would have essentially zero
capability against the most likely emerging threat-- an ICBM from
North Korea. And it would have strictly zero capability against
the much more realistic and important threat from North Korea,
Iran, or Iraq-- short-range cruise or ballistic missiles fired
from merchant ships near U.S. shores, a nuclear weapon detonated
in a harbor, or biological warfare agent (BW) disseminated in the
United States or from a ship in harbor. We will not solve our
real national security problems so long as our primary concern is
to deploy a system that will not handle the threat that is cited
to motivate its deployment. While the U.S. might be threatened to
some extent by propaganda leaflets delivered by ICBM, and somewhat
more by chemical weapons as an ICBM payload, real strategic-level
damage would be inflicted only by BW and by nuclear payloads.
As described by General Lyles, the NMD system is intended to use a
ground-based interceptor launched from a site from within the
United States (North Dakota or Alaska) to strike reentry vehicles
above the atmosphere. With North Korea as an example, in order to
be specific, these ICBMs would have been launched toward the North
in order to fall on the United States. The rocket launch flame
will be detected by the Defense Support Program (DSP) satellites
in geosynchronous orbit within considerably less than a minute
after launch, and an approximate location of the launch site and a
direction of the missile is established in that way.
The upgraded ground-based early-warning radars would some minutes
later detect the threat missile and on the basis of these data
confirming the DSP information, interceptors would be launched.
While the interceptor is in flight, a ground-based X-band radar
with better resolution will track the reentry vehicles and to some
extent discriminate them from other objects put into space by the
missile (perhaps intentional decoys, certainly other parts of the
missile) to guide the interceptor close enough to the target
missile for the interceptor's sensor to acquire the warhead and
"to discriminate the warheads from potential decoys." Several
interceptors would need to be launched at each warhead in order to
achieve the NMD requirement to have high confidence in no ICBM
warheads impacting on U.S. soil. If the system works as stated.
In July 1998, the nine-member Rumsfeld Commission to Assess the
Ballistic Missile Threat to the United States (on which I had the
privilege to serve) issued its unanimous report, judging that
North Korea could have a true (but unreliable and inaccurate) ICBM
within a couple of years-- specifically within five years of a
decision to move forward with a program, assuming that it is
thoroughly funded with a high priority. The Rumsfeld Commission
also advised that there were other and earlier threats from
missiles of shorter range launched from ships, and observed also
that BW or CW agents could be packaged in the form of bomblets
released early in flight, that would fly separately to the target
region.
It is just this last caution which I elevate to the status of a
likelihood. It is far more effective militarily for an ICBM
payload of biological warfare agents to be arriving in the form of
individual reentry vehicles (bomblets) spread over an area 10 or
20 kilometers in extent, rather than to be delivered as 100-500 kg
of BW agent at a single point in the target area. Under the
latter condition, a very narrow plume will be produced by
wind-born BW, threatening people within the narrow plume. But if
the same payload were dispersed in the form of bomblets, a large
number of such narrow plumes, each equally lethal within its
interior, would threaten people in the target area.
Given this undisputed increase in military effectiveness, any
nation with the capability to make an ICBM and reentry vehicles
would almost surely arrange to package the BW in the form of
bomblets, released just as soon as the ICBM reached its final
velocity on ascent. Placing the bomblets at predetermined
positions in a rack within a spinning final stage, the release of
the bomblets would then allow them to spread during their
20-minute or more flight to reentry, with the initial rotation
rate determining precisely the spread, and the pattern being that
in which the bomblets were stored in the missile. This threat of
BW bomblets released on ascent is to be expected whether or not a
defense is deployed, but the proposed NMD would have strictly zero
capability against these bomblets. First, there would be so many
of them (with a loading of perhaps 1 kg of agent per bomblet) that
it would exhaust any planned number of interceptors. Second, even
with a thousand or more interceptors, it is all too easy to have
each bomblet in a loose-fitting and lumpy shell, just in order
that the ICBM could have deployed a vastly larger number of empty
such shells. This is an example of the great utility of
"antisimulation", in which the warhead itself is modified to make
it easier to simulate by a cheap and convenient decoy.
If North Korea should manage to obtain fissile material either
from its own reactors or from abroad, so as to make a nuclear
weapon that could be carried to intercontinental range by an ICBM,
it would initially have what is probably an unreliable warhead on
an unreliable missile. The warhead would be likely to miss its
city target entirely. But would a defense make any difference?
Yes, if the launching country cooperated, but not if it wished to
prevent the intercept of its nuclear warhead.
Because the NMD interceptors are all "hit-to-kill" so that they
must collide with the warhead in order to destroy it, the attacker
need not conceal the existence of the warhead but only its exact
location. This is readily done by the use of an enclosing balloon
made of aluminum-foil coated mylar that can be put together by
anyone who buys this article of commerce and spends $20 on a
hand-held tool for heat sealing the plastic to make a large
balloon. Even a balloon ten meters (33 ft.) in diameter, inflated
after the RV separates from the missile, would render it unlikely
that an interceptor would actually strike the warhead rather than
plunging harmlessly through the balloon.
The balloon would be inflated in space by a tiny charge of
gas-generating compound like that found in every automotive air
bag, but instead of deploying in a 100th of a second or less, the
balloon could deploy in a second. Since the launch country might
fear that the interceptor striking the balloon might cause
sufficient disruption to expose the RV, several balloons in
sequence could be shrunk down on the RV (and would occupy very
little space with the air removed by an ordinary vacuum cleaner).
So each would be ready for deployment to hide the RV once again in
case the balloon was intercepted.
Alternatively, the launching country could deploy ten or more such
balloons over a region 10 km or more in extent, so that these
would need to be attacked one at a time. Even the dynamics of a
balloon bouncing around over an enclosed object could be simulated
in the decoy balloons with an enclosed object that weighed
extremely little in that case-- a heavier, small balloon just big
enough to enclose the RV.
The interceptor would normally track the RV by means of its
infrared (heat) emission and it could readily distinguish an empty
balloon from a balloon containing the RV, simply because the empty
balloon would be colder, while the RV would not have had time to
cool off during its 30 minutes or less of flight. But highly
reflective aluminum not only reflects light (and infrared) but it
correspondingly radiates a lot less-- about 30 times less than
does an unprepared surface. Furthermore, multi-layer insulation
is an article of commerce that can reduce the emitted heat by
another factor 50 or more. Finally, if the decoy maker wished to
have even greater confidence that sensors would not be able to
discriminate the decoy balloon from the balloon containing the RV,
a small chemical heat source could be used to mimic the 40 watts
of heat that would be emitted by the reentry vehicle shrouded in
multi-layer insulation within its own balloon.
These achievements are easy relative to the scale and cost of the
effort required to develop an ICBM, and if a country expects the
United States to have this NMD at the time of its first ICBM, then
I am confident that these countermeasures can and will be
provided.
But how about the observation that the NMD "would also provide
some residual capability against a small accidental or
unauthorized launch of strategic ballistic missiles from China or
Russia." This is not just an "observation"; I believe it is a
requirement. It is a very strange formulation for a requirement;
____________
"the system should provide ..." or "the system must provide ..."
would be more usual. So it is a requirement masquerading as an
observation. As such, it is sure to provoke decoy responses that
will vitiate the system, so long as China and Russia maintain
weapons with the intention of striking the United States either in
response to a U.S. strike on their territory or otherwise.
The extension of the deployment date of NMD from 2003 to 2005
would not help to improve the effectiveness of the system. It
might reduce the risk of deploying some kind of system that would
work against a cooperating threat from "extremely high risk" (as
the 2003 deployment has been characterized by General Lyles) to
"very high risk", but it would not solve these problems.
I believe that no deployment decision should be made (and less
development money should be spent) until one has a proposed system
that can cope with the threat.
BMDO has a structured program for considering countermeasures,
which has the result that effective countermeasures are not
considered until a system of defense is available to counter them.
But as Churchill once observed, "Occasionally it is necessary to
take the enemy into account."
The U.S. is not helpless against these threats. It can and has
done a lot to deter the development of the threat, the deployment
of such capabilities, and even the use of deployed capabilities.
Of course, showing great fear and concern simply raises the
bargaining value of one or a few ICBMs in North Korea, Iran, or
Iraq. Certainly in North Korea they are vulnerable to preemptive
strike by non-nuclear means, and, once used, any remaining weapons
would almost certainly be struck by nuclear weapons.
Against BW, passive protective means can do a lot-- by maintaining
positive pressure of filtered air in homes, business, and
factories, either at all times or on warning of attack. With ICBM
delivery, we would know where and when reentry took place, and
with proper planning and investment could counter not only the
threat of BW delivered by ICBM but also by short-range missiles or
even by dispersal from a car or truck.
Finally, it is entirely possible (especially with North Korea's
launch of ICBMs) to destroy the weapons by intercept in boost
phase-- while the first, second, or third stage of the ICBM is
still burning. DSP (or beginning in 2004 its successor, the
Spaced-Based Infrared System-- SBIRS-high) would provide data
accurate enough so that no radar would be necessary or any other
aid to the interceptor. But the interceptor would have to be
launched from a site sufficiently close and have sufficiently high
performance in order to reach the missile while it was still
burning. Furthermore, the interceptor could not simply home on
the flame but in the late stages of intercept would need to look
"ahead" of the flame, in order to strike the solid missile and not
sail harmlessly through the tenuous flame. This could be done
either by blind reckoning because of the known shape of the flame,
or by actual detection of the solid missile with a proper design
of the interceptor seeker.
Because of the vast ocean area east and north of North Korea,
North Korean ICBMs aimed at the United States are an ideal target
for ground-based boost-phase intercept. Specifically, it should
be possible to use an interceptor of the same gross launch weight
as the GBI of the NMD program (about 14 tons, with 12.5 tons of
solid fuel) to boost the kill vehicle (of perhaps 60 kg mass and
containing some 15 kg of liquid fuel) to a speed similar to that
of the ICBM-- 7 km/s, but with larger engines relative to the
mass, so it will reach its final speed more rapidly. A simple
calculation shows that the sea-based interceptor could be deployed
as much as 2100 km downrange from the launch site and still be
able to catch the ICBM while it is still burning. We assume a
burn time of 250s to ICBM speed of 7 km/s (an acceleration of
three times that of gravity-- "3 g") while the interceptor
receives 7 km/s in 100 seconds, so an average acceleration of 7 g.
Because the interceptor must rise vertically in the lower
atmosphere, it probably moves only about 250 km toward its target
while it is burning, and then in the remaining (250-100) seconds
moves some 1050 km. So in the burn time of the ICBM, the
interceptor can reach out a total of 1300 km from its launch site.
The ICBM at an average speed of 7/2 = 3.5 km/s into 50s moves no
more than 875 km from its launch site. The interceptor could be
deployed as much as 1300 km (to be practical, use 1100 km) east or
west of the ICBM trajectory, about 800-1000 km downrange. So
there is plenty of room for U.S. navy ships to carry these
interceptors. The ships need have no missile-tracking radars.
Such a sea-based boost-phase intercept system is not compliant
with the 1972 ABM Treaty, but Russia and the three other parties
to the Treaty might well agree to a specific exception, especially
if this were combined with progress on lower missile levels in
Russia and the United States.
Richard L. Garwin